1. Field of the Invention
The present invention relates to a tool for effecting drilling and/or chiseling and including a tubular shaft having an axially extending through-channel and provided, at one of its axial ends, with a drilling or chiseling head, a connection member connected with another of axial ends of the shaft, a cross-bore connecting the through-channel of the shaft with a tool circumference, and a shank provided at an end of the connection member remote from the shaft.
2. Description of the Prior Art
Tools of a type described above are used for drilling or chiseling in stone, concrete, brickwork and similar brittle materials. E.g., tools are known in which the drillings are transported from the drilled or chiseled bore via at least one helical discharge groove provided on the drilling or chiseling tool. Also known are so-called suction drilling or chiseling tools one of which is disclosed in German Publication DE 198 10 192A1. The tool described in the German Publication has a tubular shaft with an axially extending through-channel and a drilling head provided at the front, free end of the shaft which is connected, at its end remote from the drilling head, with a connection member that connects the tool with a suction device.
The suction device, which is connected with a vacuum-producing device, e.g., a vacuum cleaner, serves for removal of the drillings or chips from the drilled or chiseled bore. The suction device has a housing which surrounds the tool and into which the cross-bore, which is connected with the through-channel of the shaft, opens.
A tool of this type, in which the connection member is connected with the shaft by a conventional joining technique, insures its cost-effective manufacturing. However, its manufacturing advantage leads to its applicational disadvantage. It is to be pointed out that a tool of this type is used with a hand-held mechanized tool into which it is inserted with its shank. The mechanized tool transmits, via the shank, to the tool both rotational movement and impact translateral movement. The impacts, which are applied to the tool, often cause fracture or breaking in the transitional region between the shaft and the connection member. The danger of breaking is particularly great when tool having a small diameter are used. This is because when small diameter tools are used with hand-held mechanized tools, a larger power is transmitted to the tool as a result of impacts. The fracture or breakdown results in a premature failure of the tool long before the tool becomes unusable due to wear.
Accordingly, an object of the present invention is to provide a tool of the type discussed above in which the premature failure is prevented while manufacturing advantages are retained.
This and other objects of the present invention, which, will become apparent hereinafter, are achieved by providing a connection member a cross-sectional surface of which is at least in 2.5 times larger than the cross-sectional section of the shank.
Proceeding from a premise that the dimensioning of the shank of a tool is effected dependent on a power of a mechanized tool the working tool is used with, the dimensioning of the connection member according to the invention is based on knowledge that concentration of mass primarily in the region adjacent to the shank results in a certain absorption of the impact energy. Because of the dimensioning of the connection member according to the present invention, it absorbs so much impact energy that due to different mass characteristics of the shaft and the connection member, no breakdown in transition region between these elements takes place.
It was found that for preventing breakdowns and fractures, it is advantageous when the largest cross-sectional surface of the connection member is approximately equal to 4 times of the largest cross-sectional surface of the shank.
The danger of breakdowns is particularly great when the tool has a small diameter as in this case, the difference in mass between the connection member and the shaft is particularly crucial. Because with a small diameter tool, little impact energy is needed, the mass concentration in the region adjacent to the shank, which leads to the impact energy absorption, is particularly noticeable. In order to insure the proper dimensioning of the connection member, the diameter of the connection member should at least correspond to the diameter of the drilling or chiseling head. To achieve this prerequisite, different forms of the inventive tool are contemplated, e.g., the shaft can have a smaller diameter than the connection member. For tools having large diameters, there exists a possibility to form the shaft with a diameter that corresponds to the diameter of the connection member. In this case, the shaft mass contributes to the mass accumulation in the region adjacent to the shank, and the mass of the connection member can be reduced.
When the connection member has sufficiently large dimensions, preferably, the cross-bore is formed in the connection member, providing a connection between the through-channel of the shaft and the suction device housing that surrounds the connection member.
When it is the shaft that contributes to the mass concentration in the region adjacent to the shank, the cross-bore is preferably formed in the rear region of the shaft. In this case, the connection member can be made very short which results in its low cost and in economy of material.
In order to insure a reliable removal of drillings from a drilled bore, the through-channel and the cross-bore should have an adequately large diameter. It is particularly advantageous when the through-channel and the cross-bore have the same diameter. In order to optimize the removal of the drillings or chips from the fluidic point of view, advantageously, the cross-bore is so formed that at least a portion of the cross-bore forms with the axis of the connection member an angle from about 30xc2x0 to 70xc2x0.
When at least a portion of the cross-bore forms with the connection member axis an angle of about 45xc2x0, in addition to fluidic advantages, manufacturing advantages are achieved. An angle of 45xc2x0 can be easily formed with the existing manufacturing equipment. This advantage is achieved independently of whether the cross-bore is formed in the connection member or in the rear region of the shaft.
As it is known from the state of the art, a conventional joining technology can be used from connecting the shaft with the connection member. In order to further improve the connection between the shaft and the connection member when the conventional joining technology is used, an economical geometrical design of the elements of the tool should be undertaken. This connection is further improved when, preferably, the connection member has a journal an outer diameter of which corresponds to the inner diameter of the shaft through-channel. In this case the inner profile of the through-channel leads to the increase of the joining surface. The journal is formed as a complementary member to the inner profile of the through-channel. The journal is provided at an end of the connection member opposite the shank. Providing of the journal is particularly preferable when the connection member has a short axial end, and the cross-bore is formed in the rear end of the shaft.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.